1. Field of the Invention
The present invention relates to a lithographic pellicle that is used as a debris shield for a lithography mask when producing a liquid crystal display panel or a semiconductor device such as an LSI or a ULSI.
2. Description of the Related Art
In the production of a semiconductor such as an LSI or a ULSI or the production of a liquid crystal display panel, a pattern is formed by irradiating a semiconductor wafer or a liquid crystal master plate with light; if debris is attached to an exposure master plate used here, since the debris absorbs the light or bends the light, there are the problems that the replicated pattern is deformed, the edge becomes rough, or the background is stained black, thus impairing the dimensions, quality, appearance, etc. The ‘exposure master plate’ referred to in the present invention is a general term for lithographic masks and reticles.
These operations are usually carried out in a clean room, but even within a clean room it is difficult to always keep the exposure master plate clean, and a method is therefore employed in which a pellicle that allows exposure light to easily pass through is adhered to the surface of the exposure master plate to act as a debris shield.
In this case, the debris does not become attached directly to the surface of the exposure master plate but becomes attached to the pellicle film, and by focusing on a pattern of the exposure master plate when carrying out lithography the debris on the pellicle film does not become involved in the replication.
The pellicle is basically constituted from a pellicle frame and a pellicle film stretched over the frame. The pellicle film is formed from nitrocellulose, cellulose acetate, a fluorine-based polymer, etc., which allows exposure light (g rays, i rays, 248 nm, 193 nm, 157 nm, etc.) to easily pass through. The pellicle frame is formed from a black-anodized etc. A7075, A6061, A5052, etc. aluminum alloy, stainless steel, polyethylene, etc. The pellicle film is adhered by coating the upper part of the pellicle frame with a good solvent for the pellicle film and air-drying (ref. JP-A-58-219023 (JP-A denotes a Japanese unexamined patent application publication.) or by means of an adhesive such as an acrylic resin, an epoxy resin, or a fluorine resin (ref. U.S. Pat. No. 4,861,402 and JP-A-2001-92113). Furthermore, since an exposure master plate is mounted on a lower part of the pellicle frame, a pressure-sensitive adhesion layer made of a polybutene resin, a polyvinyl acetate resin, an acrylic resin, a silicon resin, etc. and a reticle pressure-sensitive adhesive protecting liner for the purpose of protecting the pressure-sensitive adhesion layer are provided.
The pellicle is installed so as to surround a pattern region formed on the surface of the exposure master plate. Since the pellicle is provided in order to prevent debris from becoming attached to the exposure master plate, this pattern region and a pellicle outer part are separated so that dust from the pellicle outer part does not become attached to the pattern face.
In recent years, the LSI design rule has shrunk to sub-quarter micron, and accompanying this the wavelength of an exposure light source is being shortened, that is, instead of g rays (436 nm) and i rays (365 nm) from the hitherto predominant mercury lamp, a KrF excimer laser (248 nm), an ArF excimer laser (193 nm), an F2 laser (157 nm), etc. are being used. When the wavelength of exposure light becomes shorter, the energy of the exposure light naturally becomes high. When high energy light such as an excimer laser is used, compared with the light of conventional g rays or i rays, the possibility that gaseous material present in the exposure atmosphere will react so as to form foreign matter on the exposure master plate becomes extremely high. Because of this, countermeasures such as minimizing gaseous material within a clean room, carrying out rigorous washing of a reticle, and removing gas-generating substances from materials forming a pellicle have been taken.
In particular, since the pellicle is used by affixing it directly to an exposure master plate, there is a desire for a low gas generation rate for materials forming the pellicle, that is, a reticle adhesive, a film adhesive, an inner wall coating agent, etc., which are formed from organic materials, and improvements have been made. However, cloudy foreign matter, called haze, formed on the exposure master plate cannot be eliminated completely even by washing the reticle or reducing the amount of gas generated from the materials forming the pellicle, and this causes a decrease in the yield in semiconductor production.
Furthermore, the pattern area has been increasing, and there is an increasing demand for managing the area up to the vicinity of the pellicle frame as an exposure area. Because of this, JP-A-2001-92113 discloses carrying out C chamfering for four corners of upper and lower end faces of the pellicle frame. However, the size of the C chamfering of the upper and lower end faces of a conventionally used pellicle frame causes the problem that a pressure-sensitive adhesive for adhesion of an exposure master plate protrudes from the overall width of the frame when the pellicle is mounted on the exposure master plate. Because of this, the problem of a decrease in yield in semiconductor production has not yet been solved.